1. Field of the Invention
The present invention relates to an optical pickup for recording and reproducing information with respect to an optical disk. More particularly, the present invention relates to an objective-lens driving device and a mechanism for adjusting the inclination of an objective lens which are aimed at making the optical pickup compact and thin and stabilizing the driving of the objective lens in both a focusing direction and a tracking direction.
2. Description of the Related Art
In general, an optical pickup is comprised of an objective-lens driving device having an objective lens and an optical system block for transmitting and receiving light with respect to the objective lens, and is structured such that the objective-lens driving device is mounted on a mounting base of the optical system block.
To accurately effect the recording and reproduction of information with respect to an optical disk, it is necessary to accurately set the optical axis of the objective lens perpendicular to the disk surface.
For this reason, a mechanism for adjusting the inclination of an objective lens is conventionally known (e.g., Unexamined Japanese Patent Application (Kokai) No. 62-287443) which is arranged as follows: As shown in FIG. 1, a spherically convex mounting surface 103 is made to project from a bottom surface 102a of an objective-lens driving device 102 having an objective lens 101. In addition, as shown in FIG. 2, a spherically concave mounting surface 106 is formed in a mounting base 105 of an optical system block 104, the spherically convex mounting surface 103 is fitted in the spherically concave mounting surface 106, and the inclination of the objective lens 101 is made adjustable with respect to the center (fulcrum) 107 of a sphere formed by the spherically convex mounting surface 103 and the spherically concave mounting surface 106 by means of height adjusting screws 108.
However, since the spherically convex mounting surface 103, the spherically concave mounting surface 106, and the height-adjusting screws 108 are disposed between the objective-lens driving device 102 and the mounting base 105 of the optical system block 104, the thicknesswise dimension becomes large, thereby constituting a hindrance to the attempt to make the optical pickup thin.
In addition, to accurately effect the recording and reproduction of information with respect to an optical disk, it is necessary to prevent the occurrence of unwanted resonance. To prevent the occurrence of such unwanted resonance, in a conventional objective-lens driving device 201A shown in the perspective view in FIG. 3, the position of the center of gravity of a movable section 204, which has an objective lens 202, a focusing coil 203A for a focusing direction Z, and a pair of tracking coils 203B for a tracking direction Y, is aligned with an optical axis 205, and the central axes of the focusing coil 203A and the tracking coils 203B are aligned with the optical axis 205 (e.g., Unexamined Japanese Patent Application (Kokai) No. 2-230522).
The optical pickup having this arrangement is capable of preventing the occurrence of unwanted resonance, but it is necessary to dispose a light source, a reflecting mirror, a light-receiving element, and the like below the objective-lens driving device to effect the recording and reproduction of information. Hence, it has been difficult to make the optical pickup compact and thin.
To make the objective-lens driving device compact and thin, in a conventional objective-lens driving device 201B shown in the exploded perspective view in FIG. 4, the central axes of a focusing coil 208A and a pair of tracking coils 208B are not aligned with the optical axis 205, and the focusing coil 208A and the tracking coils 208B are disposed in a magnetic gap 207 provided in a single magnetic circuit 206 (e.g., Unexamined Japanese Patent Application (Kokai) Nos. 4-102235 and 4-103038).
In addition, in the objective-lens driving device disclosed in Unexamined Japanese Patent Application (Kokai) 4-103038, to accurately drive the movable section in the direction of the optical axis (focusing direction), a focusing-driving force which is provided outside the magnetic gap is minimized, so as to prevent an unnecessary force, such as moment, from acting in the movable section. It has been thought that this focusing-driving force occurring outside the magnetic gap, i.e., the leakage flux density, should be suppressed to as low a level as possible partly for preventing interference with metallic parts such as a motor disposed in the vicinity of the objective-lens driving device.
In addition, although the conventional objective-lens driving device 201B shown in FIG. 4 is capable of making the optical pickup compact and thin, there is a drawback in that, if an attempt is made to adjust the position of the center of gravity to either one of the driving points, the other driving point is offset from the position of the center of gravity, so that unwanted resonance occurs on the offset side.
FIG. 5A shows a schematic arrangement of an optical disk apparatus portion in a magneto-optic recording/reproducing system, in which an optical disk 301 is provided with an optical pickup 304 having a magnetic head 302 on one side and an objective lens 303 on the other side. The magnetic head 302 and the optical pickup 304 are driven in the radial direction of the optical disk 301 by a head driving device 305 and a feed motor 306, respectively, and the optical disk 301 is rotated by a spindle motor 307. Among such optical disk apparatuses, those of a type in which the optical disk 301 is covered with a cartridge 308 for the purpose of protecting the optical disk 301 have come to be marketed in recent years. This cartridge-type optical disk is arranged as follows: As shown in FIG. 5B, the optical disk 301 is rotatably accommodated in a space formed between an upper shell 308a and a lower shell 308b, and the shells 308a and 308b are provided with windows 308c and 308d, respectively. When the optical disk 301 is not in use, the windows 308c and 308d are closed by a shutter 308e, and, during recording or reproduction, the shutter 308e is moved laterally to open the windows 308c and 308d and insert the magnetic head 302 and the objective lens 303 into the windows.
In the conventional optical pickup 304, as described in, for example, Unexamined Japanese Patent Application (Kokai) 61-139945, a circuit for driving the objective lens 303 in the focusing direction and the tracking direction is disposed at a position other than that below the objective lens 303, whereby a free space is formed below the objective lens 303, and a reflecting mirror is disposed at that position, thereby making the overall optical pickup 304 thin.
With such a conventional apparatus, as shown in FIG. 6A, the optical disk 301 and the objective lens 303 are opposed to each other with an interval L33 therebetween so that the optical axis of the objective lens 303 aligns with a central portion, as viewed in the rotating direction of the disk, of the window 308d of the lower shell 308b. In this arrangement, however, since a magnetic circuit 309 for effecting the positional adjustment of the objective lens 303 in the focusing and tracking directions is disposed outside the window 308d, there arises a need to provide a gap L31 between a lower surface of the lower shell 308b and an upper surface of a yoke 310 constituting the magnetic circuit 309. As a result, the distance L32 between the lower surface of the lower shell 308b and the lower surface of the magnetic circuit 309 becomes large, thereby constituting a hindrance to making the optical pickup 304 thin and compact.
FIG. 7 shows an exploded perspective view of a conventional objective-lens driving device (Unexamined Japanese Patent Application (Kokai) No. 3-212826).
A conventional objective-lens driving device 401 shown in the drawing is arranged as follows: A lens holder 403 with an objective lens 402 affixed thereto is cantilevered by being soldered onto a printed circuit board 409 in which four wires 404 inserted in an intermediate member 405 are secured to the intermediate member 405. The intermediate member 405 is mounted on a yoke base 406.
Incidentally, the printed circuit board 409 and the four wires 404 are electrically connected to each other. Electric current is allowed to flow across a focusing coil 407A and a pair of tracking coils 407B, which are arranged in the holder 403, via these four wires 404, to thereby drive the objective lens 402 in the focusing direction Z and the tracking direction Y.
To accurately effect the recording and reproduction of information with respect to the optical disk, it is necessary to prevent the occurrence of unwanted resonance.
For this reason, as shown in FIG. 8, a damping-member accommodating portion 405a is formed in the intermediate member 405, and a gel damping member 408 is filled in the accommodating portion 405a.
However, as for the conventional objective-lens driving device 401, since the intermediate member 405 is attached to the yoke base 406, and a printed circuit board 409 is secured to the intermediate member 405 by means of screws or the like, the number of component parts used is large. Hence, there has been a problem in that if the respective component parts are fixed by means of an adhesive, the number of assembling steps increases, so that the fabrication is not facilitated.
In addition, if the printed circuit board 409 is secured to the intermediate member 405 by means of screws, there have been cases where both ends of the printed circuit board 409 at portions remote from the wires 404 become lifted off due to changes in temperature and aged deterioration, as shown in FIG. 9. Hence, the four wires 404 are respectively deflected or conversely pulled, and the supporting balance becomes deteriorated, thereby resulting in changes in the angle of the optical axis of the objective lens 402 and unwanted resonance. Further, in cases where the yoke base 406 and the intermediate member 405, and the intermediate member 405 and the printed circuit board 409 are secured separately, if the bottom surface of the yoke base 406 is set as an assembling reference plane A, as shown in FIG. 10, there has been a problem in that it is difficult to set a B surface of the printed circuit board 409 perpendicular to the reference plane A, thereby making it impossible to drive the objective lens 402 with high accuracy.